Atmosphere of Pluto facts for kids
Departure shot of Pluto by New Horizons, showing Pluto's atmosphere backlit by the Sun. The blue color is close to what a human eye would have seen, and is caused by layers of haze in the atmosphere
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| General information | |
|---|---|
| Height | ~1 700 km (exobase) |
| Average surface pressure | 1.0 Pa (9.87×10−6 atm) (2015) 0.91 Pa (8.98×10−6 atm) (2020) |
| Composition | |
| Nitrogen (N2) | >99% |
| Methane (CH4) | 0.25% |
| Carbon monoxide (CO) | ~0.0515% |
| Acetylene (C2H2) | 0.0003% |
| Ethylene (C2H4) | 0.0001% |
| Hydrogen cyanide (HCN) | 10−5-10−6% |
The atmosphere of Pluto is a thin blanket of gases surrounding the distant dwarf planet Pluto. Even though Pluto is tiny and freezing cold, it has an active and surprising atmosphere. It consists mostly of nitrogen gas, along with small amounts of methane and carbon monoxide.
These gases come directly from ice on Pluto's frozen surface. When sunlight warms the ice, it turns straight into gas. This physical change is called sublimation. Pluto's atmosphere is famous for its stunning blue haze layers and wild seasonal cycles.
Pluto has an extremely low surface pressure compared to Earth. In 2015, NASA's New Horizons spacecraft measured its surface pressure at around 1 Pascal. That is about 100,000 times thinner than the air we breathe on Earth.
Contents
- What Gases Make Up the Atmosphere of Pluto?
- Why Does Pluto Have Beautiful Blue Haze Layers?
- How Is the Atmosphere of Pluto Structured?
- How Does Atmospheric Pressure Change on Pluto?
- How Do Extreme Seasons Affect Pluto's Sky?
- How Does Pluto Lose Its Atmosphere to Space?
- How Did Scientists Discover Pluto's Atmosphere?
- Images for kids
- See also
What Gases Make Up the Atmosphere of Pluto?
The air around Pluto is made of simple molecules. Sunlight breaks these gases apart to build complex chemical mixtures.
The Primary Atmospheric Gases
Nitrogen is the most common gas on Pluto, making up over 99 percent of the total air. The nitrogen ice on Pluto's surface easily evaporates into gas to feed the sky.
Methane makes up roughly 0.25 percent of Pluto's atmosphere. Even though this amount seems tiny, methane plays a huge role in warming the upper air. It acts as a powerful greenhouse gas.
Carbon monoxide makes up around 0.05 percent of the air. Carbon monoxide acts as a natural cooling agent in the Plutonian sky. Together, methane and carbon monoxide balance the temperature of the upper atmosphere.
Complex Chemicals and Tholins
High-energy sunlight and cosmic rays hit the nitrogen and methane in the upper atmosphere. This radiation breaks chemical bonds and creates brand new molecules.
Scientists have detected trace gases like ethane, ethylene, acetylene, and hydrogen cyanide. These heavier chemicals slowly drift downward and stick to the surface as frost.
Over time, radiation transforms these chemicals into reddish-brown organic molecules called tholins. Tholins fall like fine soot, giving Pluto's surface its distinctive rusty-orange color.
How Surface Ices Control the Air
Pluto's atmosphere exists in direct balance with the solid ice resting on its surface. When a substance jumps directly from solid ice to gas without melting into liquid, scientists call it sublimation.
Nitrogen ice sublimates very easily even in extreme cold. Carbon monoxide sublimates second most easily, followed by methane ice.
When Pluto gets slightly warmer, more ice turns to gas, making the air thicker. When Pluto gets colder, the gases freeze back onto the ground as fresh frost.
Why Does Pluto Have Beautiful Blue Haze Layers?
One of the greatest discoveries made by the New Horizons mission was Pluto's layered blue haze.
Discovering the Multi-Layered Haze
When New Horizons looked back at Pluto after flying past, it photographed glowing rings of light. The spacecraft discovered over 20 distinct, horizontal haze layers floating in the sky.
These haze layers stretch across the entire globe for thousands of kilometers. They extend from near the surface up to over 200 kilometers high into space.
The haze layers are separated by clear gaps of about 10 kilometers. Scientists believe atmospheric waves, caused by wind blowing over Pluto's giant ice mountains, create these organized bands.
The Chemistry of the Blue Glow
Pluto's haze looks bright blue to the human eye, very much like Earth's blue sky. This blue color is caused by the way tiny haze particles scatter sunlight.
Tiny particles floating high up measure only a few nanometers across. As these particles slowly sink, they stick together to form larger fluffy clusters.
These falling clusters become coated with organic ice compounds. When sunlight bounces off these tiny clusters, blue light waves scatter in all directions.
Mountain Shadows and Cloud Formations
Pluto's haze is dense enough to scatter sunlight onto the dark night side of the dwarf planet. In high-resolution photos, giant water-ice mountains cast long, dramatic shadows across the lower haze.
Scientists studying the data also spotted a few bright, puffy features resting close to the ground. These features might be localized condensation clouds or low-lying morning fog made of methane gas.
How Is the Atmosphere of Pluto Structured?
Pluto's atmosphere has unique temperature layers that behave very differently from Earth's atmosphere.
The Boundary Layer and Stratosphere
Near the ground, Pluto has a very thin boundary layer where the temperature is around 37 Kelvin (−236 °C).
Above this low layer lies the stratosphere. In this layer, temperatures rise rapidly with altitude instead of getting colder.
This dramatic heating happens because methane gas absorbs infrared sunlight. The temperature climbs from −236 °C at the ground to around −163 °C at an altitude of 30 kilometers.
The Mesosphere and Upper Sky
Above 40 kilometers altitude, the atmosphere enters the mesosphere, where the temperature slowly drops again.
Gases like carbon monoxide and hydrogen cyanide release heat energy back into space. This cooling balances the heating effect caused by methane.
Above 200 kilometers, the temperature settles at a steady 80 Kelvin (−193 °C). Pluto's upper air remains surprisingly stable around the entire dwarf planet.
How Does Atmospheric Pressure Change on Pluto?
Pluto's atmospheric pressure is very low, but it changes dramatically over time.
Measuring Air Pressure from Earth
Astronomers first measured Pluto's air pressure by watching it pass in front of distant stars. This astronomical technique is called a stellar occultation.
When Pluto blocks a star, its atmosphere causes the starlight to dim slowly rather than blinking out instantly. By tracking how fast the light fades, astronomers calculate the air pressure.
Between 1988 and 2015, observations showed that Pluto's atmospheric pressure tripled. This occurred even though Pluto was moving farther away from the Sun.
Direct Measurements by New Horizons
On July 14, 2015, New Horizons flew within 12,500 kilometers of Pluto's surface. The probe sent radio beams through the atmosphere back to Earth-based dishes.
These radio signals provided the most accurate air pressure measurements in history. The probe recorded a ground pressure of roughly 1.0 Pascal, confirming ground-based estimates.
In more recent years, astronomers observed new occultations. These measurements showed that the atmospheric pressure dropped slightly after 2016 as surface regions cooled down.
How Do Extreme Seasons Affect Pluto's Sky?
Pluto takes 248 Earth years to make a single orbit around the Sun. Its seasons are among the most extreme in the entire Solar System.
An Oval Orbit and Tilted Axis
Pluto has an eccentric, oval-shaped orbit. At its closest point to the Sun (perihelion), it receives almost three times more sunlight than at its farthest point (aphelion).
Pluto also has a massive axial tilt of 122.5 degrees. This extreme tilt causes polar days and polar nights that last over a century.
When a pole tilts into sunlight, frozen nitrogen vaporizes rapidly into gas. When a pole points away into darkness, gases freeze back onto the surface as fresh glaciers.
The Great Migration of Surface Ices
Pluto passed perihelion in 1989 and is now moving farther out into deep space. Shortly before perihelion in 1987, Pluto's northern hemisphere emerged from a 124-year polar night.
The sudden sunlight on northern nitrogen glaciers caused huge amounts of gas to evaporate into the air. The southern hemisphere took a long time to cool off due to stored thermal heat.
Because the south stayed relatively warm, nitrogen gas could not easily freeze there. Instead, the gas piled up in the atmosphere, creating a temporary boom in air pressure.
How Does Pluto Lose Its Atmosphere to Space?
Because Pluto is a small world with weak gravity, holding onto an atmosphere is a constant struggle.
Solar Wind and Atmospheric Escape
The solar wind is a continuous stream of charged particles flowing outward from the Sun. When solar ultraviolet light strikes Pluto's upper air, it ionizes gas molecules into charged ions.
The solar wind sweeps past Pluto, grabbing these charged particles and carrying them into space. This process forms a long plasma tail streaming behind the dwarf planet.
Instruments on New Horizons showed that Pluto loses gas much more slowly than scientists once feared. The upper atmosphere stays colder and more compact than early computer models predicted.
Sharing Atmosphere with Charon
Pluto has a giant moon named Charon, which orbits very close to the dwarf planet. Some of the escaping nitrogen and methane gas drifts across the void toward Charon.
Charon captures an estimated 2.5 percent of the gas lost by Pluto. The captured methane freezes at Charon's freezing north pole.
Solar radiation slowly processes this captured gas into reddish tholins. This process created the distinct reddish-brown polar cap on Charon known as Neverland Regio.
How Did Scientists Discover Pluto's Atmosphere?
Detecting air on a tiny world billions of kilometers away required decades of clever astronomy.
Early Telescope Observations
In the 1940s, astronomer Gerard Kuiper used powerful spectrographs to search for gas around Pluto, but found nothing. Telescopes were not yet sensitive enough.
In 1976, astronomers using the Nicholas U. Mayall Telescope in Arizona found traces of methane ice on Pluto. Since methane ice sublimates in sunlight, scientists realized a thin atmosphere had to exist.
The definitive proof arrived on June 9, 1988, during a major stellar occultation. Multiple observatories, including the Kuiper Airborne Observatory flying in an airplane, watched starlight gradually dim as Pluto passed in front.
Modern Discoveries and Spacecraft Exploration
In 1992, astronomers using the United Kingdom Infrared Telescope discovered vast fields of solid nitrogen ice across Pluto's surface. This proved that nitrogen must be the main gas in the air.
In July 2015, NASA's New Horizons spacecraft completed its historic flyby. The probe transformed our understanding of Pluto from a blurry dot into an active world with blue skies, high hazes, and changing weather.
Images for kids
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Multiple haze layers hanging over the plains of Sputnik Planitia on Pluto.
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Solar ultraviolet absorption graph showing the structure of Pluto's atmosphere.
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Potential low-altitude cloud formations spotted in Pluto's atmosphere.
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Infrared view of Pluto's glowing atmospheric envelope taken by New Horizons.
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See also
- Climate zones on Pluto
- Atmosphere of Triton
- New Horizons
